Amazing how much difference BB levels makes.
My party is
Felneus [64/100] [Medulla Gem] SBB1
Serin [80/80] [Sacred Jewel] BB8
Serin [80/80] [Sacred Jewel] BB5
Cayena [80/80] [Burny's Soul Stone] BB10
Cayena [80/80] [Divine Stone] BB6
Problem is, you have an engine powering that forward. Without that engine and high hit/output characters, it would fall apart. The unit quality in question is the most important part of the equation, level, type, and BB level are very secondary to that. If you were to swap out the serins for mega and cayena for lava, you would have very different results and point totals. You would still probably clear levels, but it would be very different score wise since you are cutting the hits in half and spacing them out instead of compressing them together.
This situation is going to remain true in frontier hunter until they change the scoring methodology for sparks, BB kills, and multi-kills. The damage assessment on top of that, in addition to the overkill scoring is like rewarding someone for getting those 3 rewards already, never mind the additional point bonus for crystal generation which is higher on higher hit count characters.
The new Lugina wave (Wave 5 of End) is stupid.
He did Ground Rock 6 times in one round. That's over 10K damage to each and every enemy, AoE. And that was with a defense potion up, and all high defense units.
I'm not entirely convinced that an all fire party that could survive that, much less anyone else.
On a defense buff party, his regular ground rock aoe only does around1k. Anima vargas 6* /w 6* support vargas and no orb buffs put his hp at above 7,200hp. His super dos a lot more, but less than 3k and his half health attack is flat out cheating. My fire units could pretty much sleep through his "normal" attacks AOE or not. His bigger AOE needed a good heal afterwards though. If the defense buff was down, he hurt a lot more too. I didn't get hit with a 6x regular AOE round, but that would be roughly equal to him doing 2 of his big AOE hits. Worst round I had was a big AOE hit followed by a small aoe and 3 normal attacks. His normal hits were doing about 40-60 damage per report against my fire units with a defense buff up.
Anytime the game does what you described, it is just deciding randomly that you should lose for whatever reason. I had similar happen to me on mid when stya did her aoe twice, along with nemia, and then attacked 4 more times on the same person destroying my chance for the survival bonus for the end of dungeon assessment, no items used bonus for that round and something else that I'm forgetting that prevented me from getting the sacred jewel reward from my one and only chance at getting a score that high to date.
